As one kind of new light sources with high-efficiency, LED (Light Emitting Diode) modules are widely applied in illumination in commercial, industrial and domestic fields due to advantages such as a long lifespan, a low energy consumption, energy-saving and environmental protection.
When the LED module acts as a light source of an illumination device, the lifespan of the illumination device not only depends on an illumination performance of the LED, but also depends on stability of driving circuit components for providing a working voltage for the LED module. In conventional application solutions, the bottleneck of the lifespan of the LED module still lies in the stability of the voltage provided by the driving circuit. In order to reduce the influence of fluctuation of the driving voltage to the lifespan of the LED module, it is necessary to design a new alternating current rectifying circuit for providing a stable driving voltage to drive the LED module based on the widely applied alternating current at present.
In a bridge rectifier circuit, semiconductor rectifier diodes (or named diodes) are connected to form a simple rectifying circuit. The bridge rectifier circuit is widely applied in various voltage-stabilizing applications for AC-DC conversion. Through the bridge rectifier circuit, the alternating current (AC) is rectified into the direct current (DC), so as to provide a relatively stable voltage for the LED module and thus lengthen the service life of the LED module.
FIG. 1 is a schematic diagram illustrating a structure of a conventional alternating current rectifying circuit for driving an LED module. The LED module is connected to a DC output terminal of the alternating current rectifying circuit. The alternating current is rectified by the alternating current rectifying circuit so as to be capable of directly driving the LED module. Referring to FIG. 1, the alternating current rectifying circuit is a bridge rectifier circuit, and includes an alternating current module (AC), a first diode D1, a second diode D2, a third diode D3 and a fourth diode D4.
A positive terminal of the first diode D1 is connected with a negative terminal of the second diode D2, and a negative terminal of the first diode D1 is connected with a negative terminal of the third diode D3 and an input terminal (V+) of an external LED module.
A positive terminal of the second diode D2 is connected with a positive terminal of the fourth diode D4 and an output terminal (V−) of the external LED module.
A positive terminal of the third diode D3 is connected with a negative terminal of the fourth diode D4.
One end (A1) of the alternating current module is connected with the positive terminal of the first diode D1, and the other end (A2) thereof is connected with the positive terminal of the third diode D3.
A cycle of the alternating current includes a positive half cycle and a negative half cycle, wherein the positive half cycle is a time period during which the alternating current ascends to a positive peak value from a zero value and descends from the positive peak value to the zero value; and the negative half cycle is a time period during which the alternating current descends to a negative peak value from the zero value and ascends from the negative peak value to the zero value.
During the positive half cycle of the alternating current, the alternating current outputted from the alternating module passes through the first diode D1, the external LED module and the fourth diode D4 so as to form a current loop for providing working voltage for the external LED module.
During the negative half cycle of the alternating current, the alternating current outputted from the alternating module passes through the third diode D3, the external LED module and the second diode D2 so as to form another current loop for providing working voltage for the external LED module.
From above, in the conventional alternating current rectifying circuit for driving the LED module, the alternating current, after being rectified by the diodes, directly drives the LED module to operate. The alternating current fluctuates periodically, and the LED module has a certain switching-on voltage, i.e., only when the voltage applied across the LED module exceeds the switching-on voltage, the LED module may be turned on and may emit light; and if the voltage applied across the LED module does not exceed the switching-on voltage, the LED module is in a cut-off status, i.e., in a status of not emitting light. Thereby, the voltage which can be provided by the conventional alternating current rectifying circuit to the external LED module when the current loop reverses its current direction is smaller than the switching-on voltage, thus the luminous efficiency of the LED module is relatively low; further, through the rectification by the diodes in the alternating current rectifying circuit, the voltage value outputted to the LED module fluctuates as the fluctuation of the alternating voltage, thereby the stability of the output voltage is relatively low, and obvious flickering phenomenon appears in the LED module, which shortens the service life of the LED module.